Using Models to Answer Questions About Systems
2 answers:
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Answer:
Approximately formula units (
).
Explanation:
Refer to a modern periodic table for the relative atomic mass of magnesium () and chlorine (
):
:
.
:
.
In other words, the mass of of
atoms would be (approximately)
.
Likewise, the mass of of
atoms would be approximately
.
One formula unit of the ionic compound includes exactly as many atoms as there are in the given formula. The formula mass of a compound is the mass of
of the formula units of this compound.
The formula includes one
atom and two
atoms.
Hence, every formula unit of would include the same number of atoms: one
atom and two
atoms. There would be
of
atoms and
of
atoms in
of
formula units.
Thus, the mass of of
formula units would be equal to the mass of
of
atoms plus the mass of
of
atoms. (The mass of
of each atom could be found from the relative atomic mass of each element.)
.
In other words, the formula mass of is
.
Therefore, the number of formula units in of
would be:
.
Multiple by Avogadro's Number
to estimate the number of formula units in
:
.
Explanation:
(a) potassium oxide with water
According to reaction,1 mole of potassium oxide reacts with 1 mole of water to give 1 mole of potassium hydroxide.
(b) diphosphorus trioxide with water
According to reaction,1 mole of diphosphorus trioxide reacts with 2 moles of water to give 2 moles of phosphorus acid.
(c) chromium(III) oxide with dilute hydrochloric acid,
According to reaction,1 mole of chromium(III) oxide reacts with 6 moles of hydrochloric acid to give 2 moles of chromium(III) chloride and 3 moles of water.
(d) selenium dioxide with aqueous potassium hydroxide
According to reaction,1 mole of selenium dioxide reacts with 2 moles of potassium hydroxide to give 1 mole of potassium selenite and 1 mole of water.